STATOR FOR AN ELECTRIC MACHINE

Abstract: A stator for an electric machine comprises a tubular unslotted ferromagnetic flux collector ring (16) and stator winding coils (18, 19, 20) having two legs which extend substantially axially along the inner cylindrical surface of the flux collector ring (16), wherein each winding coil leg being confined within an envelope (22) of a thin flexible non-conductive non-magnetizable material which is impregnated with and bonded to the next legs as well as to the flux collector ring (16) by a hot-setting resinous material.

Description: Stator for an electric machine This invention relates to a stator for an electric machine which includes a tubular unslotted ferromagnetic flux collector ring, and stator windings formed by a number of winding coils associated with the flux collector ring, wherein each of the winding coils has at least two legs which extend substantially axially along the inner cylindrical surface of the flux collector ring. A problem concerned with previous electric machines of the above type is a relatively small effective space available for the winding coil wires in relation to the total cross sectional area of the windings within the flux collector ring. This means a relatively low efficiency of the machine. One prior art method for arranging the stator windings inside a flux collector ring is described in EP 0 225 132 and comprises mounting of the winding coils on a support structure of a non-magnetisable, non-conductive material and insertion of the support structure and the windings together into the flux collector ring. In this known machine, the winding support structure takes a lot of space and reduces the effective space available for the winding coil wires. Another prior art method for building electric machine stators, see for instance EP 0 193 929, comprises the measures of locating the winding legs by their end by using threads or tape, and then introducing them together with a fiberglass sleeve into the flux collector ring and fixing them to the latter by injecting a resin material. By this known method it is very difficult to obtain an accurate orientation of the winding wires and hence a high density packing of the latters. Accordingly, the invention is intended to solve the problem of how to accomplish a stator for an electric machine with a maximum effective space available for the winding coil wires in relation to the total cross sectional area of the windings and at the same time obtain an accurate orientation of the winding coil wires inside the flux collector ring. The solution to this problem is accomplished by a stator design according to the definition stated in the following claims. A preferred embodiment of the invention is described below in detail with reference ot the accompanying drawing. On the drawing: Fig 1 shows an electric motor incorporating a stator according to the invention. Fig 2 shows a cross sectional view of a stator according to the invention. Fig 3 shows a cross sectional view of a winding coil leg envelope. On the drawing there is shown an electric motor having a laminated permanent magnet rotor 10 rotatively journalled in a housing 11. The latter comprises a tubular trunk portion 12 and two opposite end walls 13, 14. The stator of the motor comprises a tubular unslotted flux collector ring 16 which is made of a laminated ferromagnetic material, and stator windings 17. The flux collector ring 16 is laminated for reducing eddy current losses. The stator windings 17 comprise three winding coils 18, 19, 20, each having two substantially straight legs 18a, b, 19a, b and 20a, b, respectively. The legs of each coil are located diametrically opposite each other. See Fig 2. Each winding coil leg is enclosed in an envelope 22 of a thin flexible non-magnetizable material. This envelope is tube shaped and formed with an overlapping longitudinal slot 23 for introduction of the winding coil wires into the envelope. As illustrated in the drawing figures, the envelopes encircle the winding coil legs by more than 360°. Preferably, the amount of encircling is about 390° to ensure a safe confinement of the wiring during installation in the flux collector ring 16. Specific mechanical properties are required for the material used in the envelopes such that the winding coil legs may be firmly pressed together radially as well as circu ferentially without loosing too much of their preformed shape, as illustrated in Fig 3, as well as their function to align the winding legs. The envelope material must also withstand frictional forces during insertion and compressing of the coil legs. Suitable materials for this purpose are commercially available isolation materials for electric machines etc. like films and fibrous materials or hybrids thereof which easily combine with a suitable impregnating and bonding material. These materials are not only non-conductive they are also stiff enough to maintain pretty well a preformed shaped and are apt to withstand some mechanical stress and wear to protect the wiring during the installation process. The thickness of the envelope material depends to some extent on the size of the motor and ranges from 0,1 to 0,5 mm. This means that the envelope material occupies just a minor part of the space available for the windings. The radial space available for the windings in small motors may in some cases be as small as 2-3 mm's which means that the thickness of the envelope material is crusial indeed for how much effective copper wire there is room for. Before the assemblage of the stator, the winding coils 18, 19, 20 are prefabricated and wound to desired length, and the straight legs 18a, b, 19a, b and 20a, b, respectively, are wrapped in the envelopes which are prefabricated separately. The coil legs 18, 19, 20 are inserted in the flux collector ring 16 in the desired pattern, illustrated in Fig 2, and are properly located by means of a cylindrical mandrel introduced between the legs. Thereafter, an impregnating and bonding material such as a hot-setting resin is applied inside as well as outside the envelopes to fix and secure the coil legs and wires relative to the flux collector ring 16. This is accomplished by submerging the entire flux collector ring assembly into a bath containing heated resin. Preferably this bath treatment is carried out in a receptacle subjectable to pulsating pressure below atmospheric pressure. Thereby, the resin penetrates and fills up the entire space left between all copper wires within each of the envelopse and impregnates the envelope material. After setting, the resin secures the coil legs to the inner wall of the flux collector ring 16 as well as to one another. Thereby, a very compact stator winding is obtained. As may be seen in Fig 2, the coil leg confining envelopes as well as the bonding resin occupies a very small space in relation to the effective wiring, which means that the effective available space for the winding coil wires is very large in relation to the total space or cross sectional area of the coil windings within the flux collector ring 16. This effective space available for the coil winding wires constitutes more than 80 % of the total winding space.

Claims: Claims 1. Stator for an electric machine, comprising a tubular unslotted ferromagnetic flux collector ring (16) , and stator windings(17) formed by a number of winding coils (18, 19, 20) associated with said flux collector ring (16), each of said winding coils (18, 19, 20) consisting of a number of wires put together in at least two legs (18a, b, 19a, b, 20a, b) extending substantially axially along the inner cylindrical surface of said flux collector ring (16) , c h a r a c t e r i z e d i n that each of said winding legs (18a, b, 19a, b, 20a, b) is confined in a tube- shaped envelope (22) of a thin flexible non-conductive non-magnetizable material which is impregnated and bonded together with said wires in each of said winding legs (18a, b, 19a, b 20a, 20b) by a hot-setting resinous material, said envelope (22) has a longitudinal overlapping slot (23) for insertion of said winding leg, such that said envelope (22) encircles said winding leg by more than 360°. 2. Stator according to claim 1, wherein the effective space available for the winding coil wires consitutes more than 80 % of the total cross sectional area of said windings within said flux collector ring. 3. Stator according to claim 1 or 2, wherein said winding coil legs are fixed and secured to said flux collector ring (16) as well as to one another by bonding with said hot-setting resinous material. 4. Stator according to anyone of dims 1-3, wherein said envelope material has a thickness in the range of AMENDED CLAIMS [reveived by the International Bureau on 17 October 1994 (17.10.94); original claims 1,3,5,6 amended; remaining claims unchanged (2 pages)] 1. Stator for an electric machine, comprising a tubular slotless ferromagnetic flux collector ring (16) , and stator windings(17) formed by a number of winding coils (18, 19, 20) associated with said flux collector ring (16), each of said winding coils (18, 19, 20) consisting of a number of wires put together in at least two legs (18a, b, 19a, b, 20a, b) extending substantially axially along the inner cylindrical surface of said flux collector ring (16) , c h a r a c t e r i z e d i n that each of said winding legs (18a, b, 19a, b, 20a, b) is confined in a tube- shaped envelope (22) of a thin flexible non-conductive non-magnetizable material which is impregnated and bonded together with said wires in each of said winding legs (18a, b, 19a, b 20a, 20b) by a hot-setting resinous material, and said winding coil legs are fixed and secured to said flux collector ring (16) as well as to one another by bonding with said hot-setting resinous material. 2. Stator according to claim 1, wherein the effective space available for the winding coil wires consitutes more than 80 % of the total cross sectional area of said windings within said flux collector ring. 3. Stator according to claim 1 or 2, wherein said envelope (22) has a longitudinal overlapping slot (23) for insertion of said winding leg, such that said envelope (22) encircles said winding leg by more than 360°. 4. Stator according to anyone of dims 1-3, wherein

Inventors: HANSSON GUNNAR CHRISTER, HANSSON, GUNNAR, CHRISTER
Applicants: ATLAS COPCO TOOLS AB, HANSSON GUNNAR CHRISTER, HANSSON, GUNNAR, CHRISTER
Application year: 1994
Main classification: H02K3
IPC codes: H02K3, H02K15